This invention relates to polymers that are of particular value as flocculants for suspensions of organic matter of a proteinaceous or cellulosic nature such as are to be found in sewage and industrial plant treatment effluents or in paper mills.
It is commonly accepted that such suspended materials which are hydrophilic in nature and which often have specific gravities quite close to that of the aqueous liquors in which they are suspended, contrast in a marked way with the more hydrophobic mineral suspensions in that they are frequently found to be much more difficult to flocculate economically with chemical reagents prior to a physical dewatering step such as filtration, flotation, sedimentation, dewatering or in the retention of such materials for processing. These difficulties are particularly noticeable when higher proportions of suspended matter are present, commonly involving concentrations of 0.5 percent by weight and upwards wherein the suspensions take on a paste-like consistency and are commonly described as sludges or paper furnishes.
It is well known that the clarification or dewatering of sewage and industrial sludges and similar organic suspensions may be aided with the use of chemical reagents, added in order to induce a state of coagulation or flocculation which facilitates the process of solid/liquid or liquid/liquid separation from water. For this purpose, lime or salts of iron or aluminum have been utilized. More recently synthetic polyelectrolytes, particularly certain cationic copolymers of acrylamide, have been found to be of interest.
Cationically charged water soluble or water dispersible polymers are utilized in a variety of processes that involve the separation of solids or immiscible liquids dispersed or suspended in water from water, and the dewatering of solids containing water. These types of polymers, which may be natural or synthetic, are broadly termed coagulants and flocculants. These polymers can be utilized in such diverse processes as emulsion breaking, sludge dewatering, raw water clarification, drainage and retention aids in the manufacture of pulp and paper, flotation aids in mining processing and color removal.
Polymers of this type generally work by neutralizing the anionic charge of the suspended solids, or liquids, which are to be removed. These solids or liquids may be waste which must be removed from water, or desirable products which are recovered from aqueous systems, such as coal fines, which can be coagulated or flocculated and sold as fuel.
In the water treatment field of solids/liquid separation, suspended solids are removed from water by a variety of processes, including sedimentation, straining, flotation, filtration, coagulation, flocculation, and emulsion breaking among others. Additionally, after suspended solids are removed from the water they must often be dewatered so that they may be further treated or properly disposed of. Liquids treated for solids removal often have as little as several parts per billion of suspended solids or dispersed oils, or may contain large amounts of suspended solids or oils. Solids being dewatered may contain anywhere from 0.25 weight percent solids, to 40 or 50 weight percent solids material. Solids/liquid or liquid/liquid separation processes are designed to remove solids from liquids, or liquids from liquids.
While strictly mechanical means have been used to effect solids/liquid separation, modern methods often rely on mechanical separation techniques which are augmented by synthetic and natural cationic polymeric materials to accelerate the rate at which solids can be removed from water. These processes include the treatment of raw water with cationic coagulant polymers which settle suspended inorganic particulates and make the water usable for industrial or municipal purposes. Other examples of these processes include the removal of colored soluble species from paper mill effluent wastes, the use of organic flocculent polymers to flocculate industrial and municipal waste materials, sludge recovery and emulsion breaking.
Regarding the mechanism of separation processes, particles in nature have either a cationic or anionic charge. Accordingly, these particles often are removed by a water soluble coagulant or flocculent polymer having a charge opposite to that of the particles. This is referred to as a polyelectrolyte enhanced solids/liquid separation process, wherein a water soluble or dispersionable ionically charged polymer is added to neutralize the charged particles or emulsion droplets to be separated. The dosage of these polymers is critical to the performance of the process. Too little ionically charged polymer, and the suspended particles will not be charge neutralized and will thus still repel each other. Too much polymer, and the polymer will be wasted, or worse, present a problem in and of itself.
Examples of such cationic polymers for dewatering include U.S. Pat. No. 3,409,546 which describes the use of N-(amino methyl)-polyacrylamides in conjunction with other cationic polymers for the treatment of sewage sludges; U.S. Pat. No. 3,414,514 which describes the use of a copolymer of acrylamide and a quaternized cationic methacrylate ester, JP 61-106072 which describes water-soluble copolymers and another class of cationic polymers used to dewater sludges described in U.S. Pat. No. 3,897,333. Utilization of polyethyleneimines and homopolymers of cationic acrylates and methacrylates and other cationic polymers such as polyvinyl pyridines is also known.
Another example of a cationic polymer useful for sludge treatment is U.S. Pat. No. 4,191,645, in which cationic copolymers prepared from a nonionic monomer, such as acrylamide, and a cationic monomer, such as trimethylammonium ethylmethacrylate methyl sulfate quaternary (TMAEM.MSQ) or dimethylaminoethylacrylate methyl sulfate quaternary (DMAEA.MSQ) are disclosed. Further examples of polymeric treatments for sludge dewatering include the 1,4-dichloro-2-butene dimethylamine ionene chloride polymer as disclosed in U.S. Pat. No. 3,928,448 and the block copolymers disclosed in U.S. Pat. No. 5,234,604.
Among treatments useful for improving retention and drainage are those described in U.S. Pat. Nos. 5,126,014 and 5,266,164.
Notwithstanding the variety of commercially available polymers which have been found to be capable of flocculating or coagulating solids sludges, there are various circumstances which tend to limit the usefulness of these reagents. While for certain sludges economical treatments with these known reagents are feasible, more often sludges require very high and cost-ineffective dosages of reagents for successful treatment. Moreover, variations often occur in sludge from any one source. For example, variations in the supply of material to the waste water/sludge/paper furnish process water and/or in the oxidizing conditions that may be involved in the production of these waters lead to a variety of particle types which must be removed. Furthermore, it is not uncommon to encounter sludges which are, for some reason, not amenable to flocculation by any of the known polymeric flocculating agents. It is therefore an object of the invention to provide to the art a superior method for the dewatering of sludge-containing industrial waste waters or in the retention of industrial processing aids.